1. Field of the Invention
Disclosed herein is a photosensitive polyimide composition, a polyimide film, and a semiconductor device using the same. Disclosed herein too is a photosensitive polyimide composition, a polyimide film, and a semiconductor device using the same, in which a polyhydroxyimide is used as a base resin. The polyhydroxyimide is mixed with a photoacid generator and a cross-linking-agent. The film of the photosensitive polyimide composition can be cured by heating.
2. Description of the Related Art
A photosensitive polyimide is polyimide that is sensitive to light or similar radiation. When the photosensitive polyimide is applied to a stress buffer layer or an interlayer insulating film during a semiconductor fabrication process, photoresist processes can be performed to form a pattern of the polyimide.
Also, resolution and miniaturization are being emphasized in semiconductor chip packaging by the recent trend towards thinner and light weight packaging. In this respect, recent developments have focused on chip scale packaging (CSP) technology. At present, the CSP technology is being developed and applied to the semiconductor chip package at various levels. In particular, recent developments have focused on wafer-level CSP technology, which finishes a chip package on a wafer.
A wafer-level CSP of the prior art is shown in FIG. 1. As shown in FIG. 1, in a wafer-level CSP, a semiconductor chip 110, which comprises an integrated circuit, is connected to a solder ball 180 through an input and output pad 120 and a redistribution layer 160. This structure is made in a batch process at the wafer level. In addition to input and output pad 120, a fuse box 130 is formed on the semiconductor chip 110. Inert layer 140 is formed on portions of semiconductor chip 110 other than the fuse box 130 and input and output pad 120. Formed on inert layer 140 is a first polymer layer 150. First polymer layer 150 is partially removed and then redistribution layer 160 formed along the top surface of the first polymer layer 150, such that redistribution layer 160 is disposed on the exposed portion of input and output pad 120. The redistribution layer 160 is then covered with a second polymer layer 170. The second polymer layer 170 is partially removed and solder ball 180 formed on the exposed portion of redistribution layer 160. Also, the redistribution layer 160 can be varied to accommodate the wafer-level CSP configuration. For example, an under bump metallurgy (UBM) can be formed in a region where the solder ball 180 is formed.
FIG. 2 shows a prior art fabrication process of the prior art wafer-level CSP illustrated in FIG. 1. Referring to FIG. 2, after the first polymer layer 150 is deposited and patterned in process S210, metal is sputtered on the first polymer layer 150 in process S220, and then etched to form a trace and a pad, thereby forming the redistribution layer 160. Subsequently, the second polymer layer 170, which covers the redistribution layer 160 and the first polymer layer 150, is deposited and patterned through in process S230, and then a solder ball 180 is arranged on the exposed redistribution layer 160 in process S240. Subsequently, in process S250, soldering is completed using reflow soldering.
As described above, in wafer-level CSP technology, peripheral input and output pads are redistributed as an array of solder terminals using thin film processes. This redistribution can mitigate the problem of resolving integrated circuit peripheral terminals.
Photosensitive polyimides can be classified into a negative type and a positive type. Examples of negative photosensitive polyimides are disclosed in U.S. Pat. No. 3,957,512 to Kleeberg et al. (hereinafter “'512”) and U.S. Pat. No. 4,243,743 to Hiromoto et al. (hereinafter “'743”). The '512 patent discloses a polyamic acid where a photosensitive functional group is coupled with a polyimide precursor by ester bonding. The '743 patent discloses a photosensitive polyimide where a photosensitive group and a compound having amino component are coupled with a polyamic acid by ion bonding. The '512 and '743 patents disclose that when a resist composition solution including polyimide is coated on a wafer, and then exposed to light, photopolymerization occurs in the portion where the resist composition solution was exposed, so that cross-linking occurs between precursor molecules, causing the resist composition solution to become insoluble. The resist composition is developed using an organic solvent to remove the unexposed area, and then the imidization reaction is completed by heating to obtain a polyimide layer with the desired pattern.
However, while not being limited by theory, such negative polyimide photoresists have problems in that their resolution is poorer than that of positive polyimide photoresists, and the resists, or related resist formation or stripping processes, are likely to generate a defect. Also, since an organic solvent, such as N-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAc), is used as a developing solution for negative polyimide photoresists, in addition to high cost, their use is undesirable because of their environmental impact. For at least these issues, in summary, a positive polyimide photoresists that can be developed in an alkaline aqueous solution would be preferred for semiconductor processes.
Examples of positive polyimide photoresists are disclosed in Japanese Patent Publication Nos. 52-13315, 62-135824, 60-37550, and 7-33874, wherein Japanese Patent Publication Nos. 52-13315 and 62-135824 disclose a method for manufacturing a pattern using the difference in dissolution speed between an exposed area and an unexposed area, by mixing a polyimide precursor, specifically a polyamic acid, with a dissolution inhibitor, specifically a naphthoquinonediazide compound. Japanese Patent Publication No. 60-37550 discloses a photosensitive polyimide where a photosensitive group, specifically o-nitrobenzelester group, is coupled with a polyimide precursor by ester bonding. Japanese Patent Publication No. 7-33874 discloses a chemically amplified composition manufactured by mixing a resin with a photoacid generator, the resin being obtained by substituting a functional group that can be dissociated by an acid for a carboxylic group of polyamic acid.
In prior art positive polyimide photoresist technologies, the pattern is formed by a photolithography process wherein a precursor, comprised of polyimide, is converted into polyimide through a curing process at a temperature of 300° C. or greater. However, without being limited by theory, it is thought that such processes, when employed in wafer-level CSP, cause defects in integrated semiconductor devices, in part due to the high temperature of curing processes. For this reason, a positive polyimide photoresist that offers a lower temperature curing process is needed.